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Discussion Starter #1
HI Everyone,
New here and hoping someone here will have some information that will point me in the right direction. I have been trying to trouble shoot a stalling issue with my sentra. So far this is what I know.

Starts fine.
Idles fine while warming up in Open Loop. Around 825 in park and 750 in drive.
After a few minutes of warming up with temp below 170, runs fine and drives fine.
Once temp reaches around 170+ and I come to a stop and let it idle. It will be in Closed Loop at around 750RPM and Idles fine. But after 30 seconds it drops into Open Loop and will drop in RPM by around 75 down to 675 or lower and begin to stall out.

This seems to be worse under warmer temperatures. Didn't stall with ambient temps at 65-70, but ambient temps in the 80+ range and it would stall consistently when dropping back to Open Loop at idle and in drive. The RPMs still drop in open loop when in park, but not low enough to stall.

I have changed the plugs, PCV valve and hose, isolated the brake booster to see if that corrects it. Still there.
Tested the voltages on the MAF. All seem normal and voltage ranges from 1.35 to 2.1 Idle to 2500RPM.

I am getting a P0455 from time to time right now. Can this cause this problem? I would suspect that a vacuum leak would always cause an issue, not just when switching between open and closed loop. Or is that not true?

I feel like I have a lot of information, but no right direction as to where to look or test next. I don't want to start throwing parts at it. I'm using a scangauge to monitor the vehicle while driving and to pull codes.

If anyone can provide some further direction, I would really appreciate it.
I'm essentially a DIYer who enjoys finding solutions, but only have so much time to dedicate to it before hauling it into the mechanic.
Thanks so much.

Scott
 

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The stalling problem on sentras has commonly been a bad cam/crank sensors (more so the crank). Has that ever been replaced? I doubt an EVAP code would cause that, the evap code you have however.. might require some investigating, I'd have to pull up a diagram of how the EVAP system is routed in the QG18 (your engine code). Just wanted to post something to get your brain going.
 

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The stalling problem on sentras has commonly been a bad cam/crank sensors (more so the crank). Has that ever been replaced? I doubt an EVAP code would cause that, the evap code you have however.. might require some investigating, I'd have to pull up a diagram of how the EVAP system is routed in the QG18 (your engine code). Just wanted to post something to get your brain going.
Thanks for the info and the diagram. I have seen that diagram before when I had to replace the vacuum cut valve bypass valve a while back. It's been years though.
I may have created a bigger issue for myself which will take a lot longer for me to remedy, buy it's doable.
I though I would take a look at the vent control valve and give it a good cleaning since I already looked at the filler cap, cleaned the o-ring and the filler neck and reseated the cap. While under the car I noticed that one of the bolts was missing from the vent control valve and I remembered that I had snapped it off the last time I was trying to troubleshoot an evap issue. I soaked the other bolt with penetrating oil and tried very hard not to break it, but it too broke. So now I have two broken bolts. I'll need to pull the entire canister and extract the bolts so I can rotate the VCV and remove it. Then replace the screws. I did notice that the plastic on the canister is cracked where the bolt for the VCV went into it so I can't help but wonder if there is a leak there as well. I hate to spend the money getting it smoke tested if I can just pull it, clean it and put it back.
Any tips? Hoping not to break any other bolts in that process.

As for the stalling issues, I thought they might be related since it was my understanding that the evap system worked on the same vacuum system the engine does and so I thought a leak in the evap could also cause a vacuum leak. Is this not the case?

This morning I started the car and it was a lot colder and it stalled in open loop during warm up. First time that has happened. I'm still a little suspicious of the MAF, but since the car doesn't run bad at speed when warm. Although, how much is the MAF used at that point? Is it only active under open loop?

I think I'll straighten out the EVAP issue first and then go from there. I'm still able to drive it. Just have to be careful at stops. Thanks for the info.
-Scott
 

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In open loop the car is reliant more so on the MAF and the Fuel/timing table vs closed loop which is running off the o2 sensors.

The best thing to do (as you said) is to figure out that EVAP leak, it appears to be the underlying cause of all your problems, except maybe for the stalling? but you have a point it does operate on vacuum so I can see it screwing with your idle. Wish I had more advice for ya been a few years since I've owned a 1.8 sentra, and last time I messed with an EVAP system on a car I gave up. (Friends car), Ultimately he just got his ECU chipped (Honda) and turned off all the smog devices and monitors. Besides the point... keep us posted.

Are your bolts rusted or something? that they are breaking off?
 

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Discussion Starter #6
Are your bolts rusted or something? that they are breaking off?
Yea, I'm going to focus on the evap system first. Bolts were rusted. Even soaking them in penetrating oil didn't help.
Next weekend I'll have time to dig into it. Will post back what the result is after cleaning the vent control valve.
I'm also having an issue of the car not starting after filling the gas tank. Could that be an issue with the vent control valve?
I'll take it one issue at a time and see what happens.
-Scott
 

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Yea, I'm going to focus on the evap system first. Bolts were rusted. Even soaking them in penetrating oil didn't help.
Next weekend I'll have time to dig into it. Will post back what the result is after cleaning the vent control valve.
I'm also having an issue of the car not starting after filling the gas tank. Could that be an issue with the vent control valve?
I'll take it one issue at a time and see what happens.
-Scott
you're just having all kinds of funky issues.... have you tried priming the car before starting it?
 

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Discussion Starter #8
you're just having all kinds of funky issues.... have you tried priming the car before starting it?
So yesterday I tackled the P0455 code by pulling the Evap canister and the Vent Control Valve. With the two bolts broken off I had to cut the valve off by hacksawing the broken bolts from the two sides and then drill and tap the canister. The valve tested ok, opening and closing and blowing through it showed no signs of leaking.
However, with the valve in place, blowing into the evap can would result in some air passing the o-ring. Replacing the oring helped, but some leaking was still visible (Used soapy water spray). With a lot of time into this, I put it back together with the new bolts and after that, the leak appeared to be gone. Before that it was audible when blowing into the canister, but not after fully assembling it. It's all back together now, DTC reset and waiting for a drive cycle to complete. Will also be interesting to see if the starting problem at fillup goes away.

On the issue with the stalling. My next thing to try will be cleaning the intake manifold. My thought there is if it isn't closing and opening properly then it will throw off the reading from the MAF when switching to open loop.
One thing I have noticed is that when I take my foot off the gas on a long downhill on a highway, when I get back on the gas the pedal will take a bit of force to "break loose" and then press down. But then will be fine after that. I'm thinking that the flap on the intake is sticking.
Thoughts? Am I looking in the right direction or barking up the wrong tree?

Thanks.
 

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On the issue with the stalling. My next thing to try will be cleaning the intake manifold. My thought there is if it isn't closing and opening properly then it will throw off the reading from the MAF when switching to open loop.
One thing I have noticed is that when I take my foot off the gas on a long downhill on a highway, when I get back on the gas the pedal will take a bit of force to "break loose" and then press down. But then will be fine after that. I'm thinking that the flap on the intake is sticking.
Thoughts? Am I looking in the right direction or barking up the wrong tree?

Thanks.
Jeez quite a bit of work there...is the evap canister near the gas tank or in the engine bay (forgot).

Just be careful when messing with the intake manifold/throttle body, if i recall correctly your 1.8 is drive by wire (fancy term for electronic throttle) and cleaning any part of the IM or TB will mess up your idle (and may require an idle relearn). In terms of the throttle sticking... since it is electronic there is no cable that runs from the pedal to the throttle body, just a part of the wiring harness. I would remove the carpet and make sure nothing is physically stuck underneath the pedal, or remove your air box and check the throttle body for any obstructions (push the plate with your fingers, it shouldn't get stuck). It sounds like it's the actual pedal though....I would check it because that sounds dangerous. For safety though if your pedal gets stuck at wide open throttle the ECU will automatically reduce throttle input as soon as the brake is touched.
 

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Jeez quite a bit of work there...is the evap canister near the gas tank or in the engine bay (forgot).

Just be careful when messing with the intake manifold/throttle body, if i recall correctly your 1.8 is drive by wire (fancy term for electronic throttle) and cleaning any part of the IM or TB will mess up your idle (and may require an idle relearn). In terms of the throttle sticking... since it is electronic there is no cable that runs from the pedal to the throttle body, just a part of the wiring harness. I would remove the carpet and make sure nothing is physically stuck underneath the pedal, or remove your air box and check the throttle body for any obstructions (push the plate with your fingers, it shouldn't get stuck). It sounds like it's the actual pedal though....I would check it because that sounds dangerous. For safety though if your pedal gets stuck at wide open throttle the ECU will automatically reduce throttle input as soon as the brake is touched.
Yea, but better than paying for a new valve and canister.

My car is not Drive by wire. It has throttle cables. The throttle is not sticking open but rather closed. It takes extra pressure to get it to go. Never sticks at any other position but when my foot is fully off the pedal. That's why I suspect the gunked up IM.
 

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Yea, but better than paying for a new valve and canister.

My car is not Drive by wire. It has throttle cables. The throttle is not sticking open but rather closed. It takes extra pressure to get it to go. Never sticks at any other position but when my foot is fully off the pedal. That's why I suspect the gunked up IM.

Ahh I see. So the first 1.8's were cable throttle. Interesting, clean the sucker out then. :D
 

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Ahh I see. So the first 1.8's were cable throttle. Interesting, clean the sucker out then. :D
Yea, went for it today. A lot of obvious buildup. Seemed to alleviate the throttle stickiness, but not the idle issue in open loop. I then pulled the MAF again and soaked it with MAF cleaner. I performed an Idle Air Relearn afterwards and still no luck.
Is it possible for a MAF to be faulty only at idle and perform just fine at all other times? Or is it a non issue at other times since it is in closed loop? The car also hesitates quite a bit when warming up and is still in open loop so I guess the MAF would be suspect there as well. Really tempted to throw a MAF in it. Pretty big gamble.
Also found this thread on another forum.
sentra p0171 p0174 rough idle after start - Nissanhelp.com Forums
Sounds exactly like my issue so I'm going to throw in the MAF and see how it goes.
Will post back tomorrow with the results.
 

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Ok, so here is the update. New MAF installed and the problem is gone. Fingers crossed it will remain so. The interesting part however is that it no longer cycles between open and closed loop every 30 seconds at idle. It stays in closed loop. Warm up in open loop is smooth and I'm no longer getting a bouncing RPM gauge when decelerating. When the car would drop below around 40 MPH the torque converter would disengage and the RPMs would drop, but they would bounce up and down by around 200 RPM until I would either step in the gas or come to a stop.
Anyway, wanted to let everyone know what worked, after all this chasing around and around. Hopefully the evap canister code will remain gone as well. Will see. Also hoping that the P0171 that I get in the cold temps also stays away.
Thanks for the tips.
 

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Ok, so here is the update. New MAF installed and the problem is gone. Fingers crossed it will remain so. The interesting part however is that it no longer cycles between open and closed loop every 30 seconds at idle. It stays in closed loop. Warm up in open loop is smooth and I'm no longer getting a bouncing RPM gauge when decelerating. When the car would drop below around 40 MPH the torque converter would disengage and the RPMs would drop, but they would bounce up and down by around 200 RPM until I would either step in the gas or come to a stop.
Anyway, wanted to let everyone know what worked, after all this chasing around and around. Hopefully the evap canister code will remain gone as well. Will see. Also hoping that the P0171 that I get in the cold temps also stays away.
Thanks for the tips.
I wouldn't be surprised if that was the original MAF that came with the car. Well done (hopefully not premature). Hope you're car stays running. :) You ever try cleaning the MAF prior to putting a new one on? They sell a MAF cleaner, just to see if it would make a difference.
 

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I wouldn't be surprised if that was the original MAF that came with the car. Well done (hopefully not premature). Hope you're car stays running. :) You ever try cleaning the MAF prior to putting a new one on? They sell a MAF cleaner, just to see if it would make a difference.
It was the original. Tried cleaning it multiple times. No good. Odd thing is that I probed it and got good voltage readings. So something else was up with it. I picked this one up from autozone for $139. Hopefully it will last.
 
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